This invention relates generally to a photographic color printer system and more particularly to such a system capable of deriving, utilizing, and storing digital color value and print exposure data for the accurate reproduction of prints.
Conventional color printer systems have been known to combine an additive-type color printer with a microprocessor or digital system for controlling the source intensity for each primary color of incident light in the printer. For example, in one form of an additive printer, light from a lamp source for each primary color is added together to produce incident light illuminating a frame of film to be printed. As an example, the Gyori U.S. Pat. No. 4,068,943 shows an additive colorhead having color sensors in the mixing chamber for providing analog signals to be compared in a feedback loop with signals derived from digital values keyed in through a keyboard. The feedback loop controls the power applied to each color source lamp until the measured intensity for each color corresponds to the keyed-in digital color value. However, this system provides a digital display of only the keyed-in values, and cannot be used to directly measure and quantify the color values in a desired color mixture of incident light nor to program the functions of the printer in accordance with such measured or other derived values.
Another form of color printer, such as described in the Meyer et al U.S. Pat. No. 4,150,894 or Amano et al. U.S. Pat. No. 3,888,580, automatically processes a series of original frames by measuring the color density of each frame and computing the desired exposure parameters for each frame. The exposure information is stored in memory and used during the printing of each corresponding frame. Conventional color printers also employ the subtractive mode of adjusting the color mixture in the incident light of the printer. As shown in the Barbieri U.S. Pat. No. 4,165,175, for example, such systems typically employ the mechanical positioning of blocking filters in the path of a source beam of white light in order to selectively subtract from the intensity of a particular primary color. The mechanical positioning of the filters is accomplished usually with a gear or threaded screw drive. The current state of the art in subtractive colorheads is to display the color values in terms of the amount of filtration indicated on dial indicators or counters that are mechanically coupled to the filter drives. The color content of the incident light is thus subject to wide variations due to mechanical tolerances, the voltage to or condition of the source lamp, and differences between printer units.
In summary, none of the known color printers have the capacity to provide standardized, calibrated quantifications and a digital display of actual measurements of the color values of the incident or source light, or to program the functions of the printer in accordance with such measured or other derived color values. This deficiency precludes the accurate programming of a color printer in accordance with standardized values or, particularly in a subtractive-type printer, the reproduction of an exact color mixture of incident light in the same or another printer.